Metabolic diets with fats are fed and lipoprotein and apolipoprotein levels determined. Marked interindividual variation in LDL cholesterol responsiveness to dietary changes have been noted. An attempt is being made to correlate diet responsiveness with age, sex, apo I phenotype, ad- lib lipoprotein levels, body mass index and DNA markers. Drug effects on LDL cholesterol levels are being assessed on high and low fat diets.